It has been suggested that the advantages of surface-acoustic-wave (SAW) devices and the advantages of charge-coupled devices (CCD) can be utilized in an overall device using a combination of both, which overall device can be arranged to compensate for some of the individual limitations in certain applications of each of these two classes of devices.
A first suggestion for the use of such devices was set forth in the article "Charge-Coupled Devices: SAW/CCD Buffer Memory", Solid State Research Report, published by Lincoln Laboratories of the Massachusetts Institute of Technology, No. ESD-TR-77-294, pp. 37-39, 1977. In the article an integrated buffer memory was proposed utilizing a SAW input section and a CCD output section appropriately arranged to interact so as to provide a fast-in, slow-out buffer memory operation.
In such structure a substrate of p-type silicon is mounted adjacent a SAW piezoelectric substrate and has imbedded therein a plurality of n.sup.+ -type silicon sampling fingers. Such fingers are separated by boron channel stops within the silicon substrate. The sampling fingers are appropriately precharged to a desired potential and a wide-band signal is entered at an input transducer of the SAW device so as to generate a propagating surface acoustic wave having a piezoelectric displacement field above the surface of the SAW substrate. Such field modulates the potential on each of the sampling fingers and, thus, modulates the charges in the storage wells of the CCD electrodes which are coupled thereto.
Such a system using combined SAW/CCD devices as described therein, however, tends to give rise to undesirable distributed leakage problems which distort the charges in the wells of the CCD device and produce inaccurate buffer storage characteristics. Nor does the article disclose any uses for the overall device other than as a buffer storage element.